In a PDP, ultraviolet rays generated by gas discharge excite phosphors and cause them to emit light for color display. The PDP is structured so that display cells partitioned by ribs are provided on a substrate thereof, and a phosphor layer is formed on each of the display cells.
The PDPs are roughly classified into an AC type and a DC type in terms of driving methods thereof. Discharge systems thereof include two types, i.e. a surface discharge type and an opposite discharge type. Having higher definition, a larger screen, and simpler manufacturing method, a surface discharge type having a three-electrode structure is mainly used in PDPs. This type of PDPs is structured to have adjacent parallel display electrode pairs on one of substrates, and address electrodes, ribs, and phosphor layers arranged in a direction so as to intersect the display electrodes on the other substrate. This structure can thicken the phosphor layers and thus is suitable for color display using phosphors.
Such a PDP is capable of display data faster than a liquid crystal panel. Additionally, it has a larger angle of field, and higher display quality because it is a self-luminous type, and the size thereof can easily be enlarged. For these reasons, especially such a PDP has been drawing attention recently and finds a wide rage of applications, as a display device in a place many people gather or a display device with which people enjoy images on a large screen at home.
Generally, such a PDP is manufactured by the following steps. First, address electrodes made of silver are formed on a rear glass substrate. On the address electrodes, a visible light reflecting layer made of dielectric glass is formed. On the visible light reflecting layer, glass ribs are formed with a predetermined pitch. After phosphor paste including a red phosphor, a green phosphor, or a blue phosphor is applied to respective spaces sandwiched between these ribs, the phosphors are fired to remove resin components or the like in the paste. Thus, phosphor layers are formed and a rear panel board is provided. Then, low-melting glass paste is applied around the rear panel board as a member for sealing with a front panel board. The panel board with the glass paste is calcined at temperatures of approx. 350° C. to remove resin components or the like in the low-melting glass paste.
Thereafter, a front panel board having display electrodes, a dielectric glass layer, and a protective layer sequentially formed thereon is placed opposite to the rear panel board so that the display electrodes and the address electrodes are orthogonal to one another via ribs. The two panel boards are fired at temperatures of approx. 450° C. and the periphery thereof is sealed by the low-melting glass, i.e. the sealing member. Then, while the panel boards are heated to temperatures of approx. 350° C., the inside of the panel boards is evacuated. After the evacuation is completed, discharge gas is introduced at a predetermined pressure. Thus, a PDP is completed.
In a conventional PDP, a rare gas containing at least xenon (Xe) is used as discharge gas. The most commonly used gas is a discharge gas containing neon (Ne) and a several percent of xenon (Xe) mixed therein. This is a high purity gas having a gas purity ranging from approx. 99.99 to 99.999%.
However, it is extremely difficult to add impurity other than rare gas in a predetermined concentration to discharge gas uniformly in a controlled manner, in order to improve discharge characteristics. The cause is as follows. Phosphor materials and magnesium oxide (MgO) serving as a protective film, which are structural materials of a PDP and in contact with discharge gas, are prone to adsorb a large amount of gas other than inert gas: thus, it is difficult to diffuse impurity gas in discharge gas in a controlled manner. Additionally, when impurity gas is only mixed in discharge gas and introduced into a panel, a large amount of impurity gas is adsorbed in the vicinity of a place where the discharge gas is introduced. This causes variations in the luminance and discharge characteristics of the panel.
Especially, BaMgAl10O17:Eu, which is commonly used as a blue phosphor, has problems, as disclosed in the Japanese Patent Unexamined Publication No. 2001-35372: it is prone to adsorb a large amount of H2O in particular and degrade by heat.
On the other hand, a PDP has a high discharge voltage of approx. 200V. In consideration of the cost of the circuit and the resistance of the panel to voltage, a lower discharge voltage is required. At the same time, more stable discharge, higher luminance, higher efficiency, and longer life are required.
The present invention addresses these problems and aims improvement in the characteristics of a PDP, such as lower discharge voltage, more stable discharge, higher luminance, higher efficiency, and longer life.